Living with an Aerobic Treatment Unit and Spray Field

B-6234
01/10
Living with an
Aerobic Treatment Unit
and Spray Field
Bruce J. Lesikar, Diane Bowen,
Justin Mechell, and Ryan Gerlich*
I
f you own an aerobic treatment unit and spray
field, you are required by law to make sure that
your system is treating wastewater adequately.
To do this, you can either contract with a company
to conduct the required system inspections, wastewater tests, and report completion and submittal to
local governmental agencies, or you can do the work
yourself.
For both options, you’ll need to know the components of your wastewater system and understand
how they work. Basic information about aerobic
systems is given in these Texas AgriLife Extension
Service Onsite Wastewater Treatment Systems series:
▶▶ Aerobic Treatment Unit
▶▶ Tablet Chlorination
▶▶ Liquid Chlorination
▶▶ Ultraviolet Light Disinfection
▶▶ Pump Tank
▶▶ Spray Distribution System
These publications are available on the Web at
https://agrilifebookstore.org/.
You also need to know the basics of aerobic
systems inspection and their maintenance. For
information on general onsite wastewater treatment
systems, see Extension publications Onsite Waste*Extension Agricultural Engineer for Biological and
Agricultural Engineering, Editor and Extension
Communications Specialist, Extension Program Specialist and
Extension Assistant, The Texas A&M University System
water Treatment Systems: Operation and Maintenance and Understanding and Maintaining Your
Septic System.
And unless you don’t mind repairing and
replacing it often or having system backups, you’ll
need to adopt household practices that will protect
and prolong the life of your system.
Performing the work yourself
An advantage of doing the inspecting, testing,
and reporting work is saving money. You also can
be certain that the work has been done properly
and the reports are filed on time. However, if you
conduct the work yourself, you will need to:
▶▶ Get informed. To maintain an aerobic onsite
wastewater treatment system properly, you
must have extensive knowledge. This knowledge can help prevent injury to yourself,
other people, the system components, and
the environment. Obtain the manufacturer’s
literature describing system components and
the particular maintenance practices from the
company’s Web site. For a list of courses for
maintenance providers on maintaining aerobic
systems, see the Texas Commission on Environmental Quality (TCEQ) Web site at http://
www.tceq.state.tx.us. For a listing of courses
offered through the Texas AgriLife Extension
Service, see the Wastewater Treatment and
Reuse Web site at http://ossf.tamu.edu.
–––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––––
Spray heads
Chlorinator
Single-compartment
trash tank
Pump tank
Aerobic
treatment unit
Figure 1. Example treatment train for residential aerobic wastewater treatment with a spray field.
▶▶ Know and abide by all state and any local
requirements for wastewater quality, testing,
and reporting.
▶▶ Inspect the system at specified intervals, usually once every 4 months, to check its operation and perform routine maintenance.
▶▶ Wear protective clothing—such as rubber
gloves, and safety glasses, goggles, or face
shields—during the inspection and testing
activities.
▶▶ Observe stringent personal hygiene practices.
▶▶ Be adequately vaccinated against diphtheria, hepatitis B, and tetanus. Also consider
protecting yourself from hepatitis A, paratyphoid, polio, and typhoid fever.
▶▶ Collect and handle the wastewater samples
properly.
▶▶ Conduct tests on the wastewater.
▶▶ Submit a report on each inspection to the
local authorized agent.
▶▶ Take measures to avoid illness and accidents.
Common hazards associated with onsite
wastewater treatment systems include diseasecausing microorganisms, electrical shock,
insects and animals, poisonous or explosive
gases, exposure to sewage through cuts and
abrasions, and confined space entry. This
work increases your risk of sickness, physical
injury, or death.
▶▶ Keep records on the system performance and
your service activities.
▶▶ Recognize the tasks that should be left to
professionals to make sure that the job is performed correctly and that you do not subject
your family to undue health risks.
▶▶ Know local service providers who can handle
the tasks you are not trained to perform.
▶▶ Acquire sampling and testing equipment such
as a chlorine DPD field test kit, profile probe
(Sludge Judge®), dissolved oxygen test kit,
pressure gauge, and a graduated container for
solids sampling tests.
▶▶ Keep on hand any manufacturer-required specialty tools and parts.
▶▶ Have common hand tools such as a cordless
drill and bit set, shovel, and wrenches.
▶▶ Keep other supplies, such as the permit/
as-built plans/specifications, governmental
forms, a calculator, the system owner’s manual, a flashlight, insect repellent, and a first aid
kit.
▶▶ Keep on hand the proper disinfectant, such as
wastewater chlorine tablets or liquid bleach, to
add to the disinfection component.
2
If you try to carry out maintenance activities that
are beyond the scope of your training, the results
could include but are not limited to voided warranties, destroyed components, additional problems
with the system, higher repair costs, personal injury,
and even death.
If you do not maintain the system properly, you
could endanger human and environmental health,
impair your wastewater system, and incur legal
action.
Human health: Because sewage can contain
disease-causing microbes, wastewater is a public
health concern.
Environmental protection: The EPA has set national
guidelines for management of onsite and wastewater
treatment systems. The guidelines are posted on the
Web at http://cfpub.epa.gov/owm/septic/home.cfm.
System reliability: All system components from the
plumbing fixtures in the home to the spray heads in
the yard must be functional within expectations.
Legal action: By law, water that leaves your property, either through runoff or by seepage into the
ground, must meet certain quality standards as
demonstrated by laboratory tests. If your wastewater
treatment system is not maintained properly, the
water will not be treated enough, and you may be
subject to fines.
▶▶ Know the kinds of contracts available. A basic
monitoring contract meets the state’s minimum requirement but requires more maintenance activities by the homeowner. Other
contracts offer more service and limit the
homeowner’s involvement in the operation,
maintenance, and monitoring of the system.
▶▶ Choose the amount of work you want to do, if
any, and make sure the contract states clearly
who is responsible­—you or the maintenance
provider—for performing the different tasks.
▶▶ Evaluate the maintenance contract. Know
exactly what services you are paying for and
what is included in the base price of the contract. Basic information on evaluating service
contracts is available in the Extension publication, Onsite Wastewater Treatment Systems:
Homeowner’s Guide to Evaluating Service
Contracts.
▶▶ Pay attention to the work being done to ensure
that you’re getting what you’re paying for.
Understanding your system
All water, including wastewater, is part of the
hydrologic cycle (Fig. 2). After the effluent is dispersed from a wastewater system, it eventually joins
ground or surface water, both of which are used as
sources of drinking water. Because of this cycle, the
water must be treated properly to protect human
and environmental health.
Contracting with a
maintenance provider
The advantages of contracting with a maintenance provider include saving you time, eliminating
the hassle of maintaining the system yourself, and
sparing you the cost of replacing a system prematurely because it was not properly maintained. It can
also ensure that reports to the government are filed
properly and on time.
The disadvantages include the costs and the
oversight of activities provided by the maintenance
provider.
If you contract with a maintenance provider, you
will need to:
▶▶ Research local maintenance providers that
provide this service.
▶▶ Understand the terms used in on-site wastewater system maintenance contracts.
Precipitation
Clouds form
Transpiration
Evaporation
Plant
uptake
Groundwater
accessed through well
Figure 2. The hydrologic cycle.
3
Runoff
Infiltration to
ground water
Aerobic treatment units can remove substantial
amounts of contaminants that are not eliminated
by the simple sedimentation that occurs in a septic
tank. The aerobic process also breaks down dissolved solids and ammonia and reduces the number
of pathogens in the waste.
tablets release chlorine gas. Do not store
chlorine tablets in the house, garage or
storage areas with metal tools.
-- Ultraviolet (UV) light is another disinfectant
for wastewater. In this process, a lamp
emits UV light into a chamber or zone as
wastewater passes through the chamber.
The UV light destroys the microorganisms in the effluent by altering their genetic
material and retarding their ability to
reproduce.
Aerobic system processes
In onsite wastewater treatment systems, microorganisms convert waste into less harmful substances—water, carbon dioxide, and new cells.
Aerobic treatment systems consist of several processes that work together to provide a high-quality
effluent:
▶▶ Removal of gross solids (trash): After the wastewater leaves the house through a pipe, it enters
a trash or septic tank, where the solids in the
wastewater settle to the bottom or float to the
surface.
▶▶ Aeration: Air is pumped into the aeration
chamber of the unit, and the wastewater
remains in the chamber long enough to allow
the microbes to convert the waste. Aerobic
systems must have a continuous supply of
oxygen to keep the microbes healthy.
▶▶ Clarification: The clarifier removes the microbial cells, cell waste, and dead cells from the
wastewater.
▶▶ Sludge return: The solids that settle in the clarifier are returned to a previous component to
be treated further.
▶▶ Disinfection: Systems using spray distribution of effluent include a disinfection unit as
part of the treatment system. In the disinfection process, disease-causing organisms
are destroyed or inactivated. However, the
wastewater is only disinfected, not sterilized
(free of all life). The main disinfectants used
in aerobic systems are chlorine and ultraviolet
light.
-- Chlorination is the most common form of
disinfection for aerobic systems. In this
process, chlorine is added to the wastewater to reduce the number of pathogens in
it. The chlorine oxidizes and destroys the
cell enzymes of the pathogens. There are
two types of chlorinators—tablet chlorinators and liquid chlorinators. Chlorine
Spray fields
In the final stages of treatment and dispersal, the
water is dispersed into the soil. Systems that spray
the effluent onto lawns are called spray fields (Fig. 3).
For these systems, the effluent must be disinfected to
reduce the risk of human exposure to pathogens.
Pump tank
Spray heads
Figure 3. Spray field components.
Although a spray field is like a lawn sprinkler, it
should be viewed very differently. The water being
distributed is treated wastewater—not drinking
water. Residents and pets should avoid contact with
it. Texas regulations specifically prohibit effluent
from being applied to vegetable gardens because
some pathogens are resistant to disinfection.
Selecting an aerobic system size
Each aerobic treatment unit is sized to treat a
specific amount of wastewater. Aerobic treatment
units are available in a range of sizes, including
those able to treat 500, 600, 750, 1,000, and 1,500
gallons per day.
4
Table 1. Sizing of wastewater aerobic treatment units for single-family residence of various sizes.
Number
of bedrooms
Square footage
of house
Texas minimum unit
capacity (gal/day)
Traditional unit
capacity (gal/day)
1 or 2
Less than 1,501
400
450
3
Less than 2,501
400
600
4
Less than 3,501
480
750
5
Less than 4,501
600
900
6
Less than 5,501
720
1,050
7
Less than 7,001
840
1,200
8
Less than 8,501
960
1,350
9
Less than 10,001
1,080
1,500
To select an aerobic unit, first determine the
amount of daily wastewater flow from your home or
small business.
The rate of daily wastewater flow is based on
the home’s square footage or number of bedrooms,
whichever is larger (Table 1). Then choose a Class I
aerobic treatment unit that can handle that amount
of flow. The TCEQ maintains a list of Class I aerobic
treatment units approved for sale in Texas. These
units are listed by company, model number, rated
treatment capacity, and requirement for a trash tank
in the treatment system.
Water-conserving fixtures can make the wastewater too strong for a system to treat adequately.
Therefore, many treatment systems are overloaded
organically (too much waste), which requires that
the sludge be removed from the systems more often
than normal.
Most residential aerobic systems can treat 500
gallons a day or 60 gallons per hour. This assumes
that the wastewater contains an amount of organic
matter common for homes; it is typically inadequate
for businesses.
contain only the products of normal activities of
a home. If other substances enter the wastewater
stream, they may disrupt the system’s performance.
The system’s ability to treat wastewater is affected
by several factors, including the system’s capacity,
the amount and strength of the wastewater, the timing of the wastewater entering the system, and the
types of materials it receives.
Sometimes an aerobic treatment system can
meet the minimum state requirement for gallons of
wastewater treated per day, but its capacity per hour
may be too small for a family’s normal activities.
For instance, if a 500-gallon-per-day system can
handle only 60 gallons per hour (1 gallon per minute),
and a normal clothes washer uses 30 to 40 gallons at
a time, the residents may have to curtail other waterusing activities when doing laundry.
To alleviate that problem, a flow equalization
tank may be placed between the trash tank and the
aeration chamber. The tank will hold the wastewater
and send it to the aerobic treatment unit at a rate it
could handle.
Know your system’s capacity. This information
should be on the permit or the control panel label
for the aerobic treatment unit. If more wastewater
enters the system than it was designed to handle, it
will not operate as intended.
In addition to the amount of wastewater that the
system can treat, the strength of the wastewater the
Protecting and prolonging
the life of your system
An onsite wastewater treatment system is
designed to treat domestic sewage from a home
or similar facility. The wastewater stream should
5
treatment train can handle is limited. If the wastewater is too strong, it can overload the system, making it unable to meet wastewater quality regulations.
Similarly, if the wastewater contains constituents
that are toxic to the microorganisms, treatment will
be affected.
ate as filler. Keep these out of the system to
improve its long-term performance.
-- Bleach additives can affect the biology of the
septic tank and the rest of the system. Do
not overuse bleach.
-- The amount of laundry done each day is also
important. Spread out the loads over time
to help the system perform at its best.
▶▶ In-home businesses can directly affect the
system. Use for daycare increases the overall
flow and can increase the use of antibacterial soaps. The system can also be affected by
other small businesses that use chemicals,
such as antique refinishing services, beauty
shops, lawn care services, photo labs, dog
grooming services, and taxidermy shops. Barbershops typically discharge large amounts of
hair.
▶▶ Prescription antibiotics and drugs are extremely
hard on the microbes in the system. Flushing
them into the wastewater system increases the
maintenance.
▶▶ Heavy use of bath and body oils can raise the fats,
oils, and grease (FOG) values in the system.
Removal or reduction of these can improve
the performance of the system.
▶▶ A garbage disposal adds to the overall loading
of the system in four ways:
-- More waste enters the treatment system.
-- Because the organic matter has not been
digested, it takes longer to break down.
-- More water is used to rinse out the sink.
-- Smaller particles take longer to settle.
Therefore, people who use garbage disposals at
home need a larger system to treat the wastewater and more maintenance activities are
required.
▶▶ Toxic drain cleaners kill the bacteria, resulting
in a limited microbial activity in the tank and
poor separating characteristics.
▶▶ Antibacterial soap also affects the biology of the
tank.
▶▶ Liquid soap tends to be easily overused and may
create problems in the system.
▶▶ Automatic cleaners (for toilets and showers) continually send chemicals into the system, which
can cause long-term problems.
Recognizing treatment interferences
An aerobic treatment unit needs a regular supply
of wastewater. To treat wastewater effectively, the unit
needs to maintain a stable population of microbes.
Any extreme influxes of wastewater flow or strength
will impair the unit’s performance.
Your system can be affected by the amount,
strength, and timing of the wastewater entering it.
These household devices, practices, and products
can alter an aerobic system’s performance:
▶▶ Water-saving devices reduce the amount of
wastewater, but they also make it stronger,
which can prevent the system from meeting
the required effluent standards.
▶▶ Whirlpool or jacuzzi tubs (inside) typically use
large amounts of water. Their use will affect
the wastewater treatment system by exceeding
the hourly flow limit of the treatment unit.
▶▶ Multi-head showers or multiple showers used at
the same time can introduce large volumes of
water into the wastewater treatment system.
A flow equalization tank and additional
treatment capacity are needed to handle the
increased amount of wastewater.
▶▶ Water-treatment devices with automatic back flushing add extra water into the system that can be
avoided.
▶▶ Some water-conditioning units add chemicals
into the effluent that can reduce the effectiveness of the biological and physical processes
in an aerobic treatment unit. This wastewater
stream may need to be plumbed around the
treatment tanks to the pump tank.
▶▶ Condensate from air conditioning units is not sewage. Route it around the system.
▶▶ Commercial ice machines can also add large
amounts of clear water.
▶▶ Laundry activities greatly affect your wastewater system:
-- Powdered detergent can plug cast-iron piping,
and some soap contains forms of benzo-
6
usage such as excessive laundry, which can result in
lower quality water passing through the system.
▶▶ Other cleaning products may also alter the treatment process. When choosing a cleaning
product, first read the label:
-- Danger means that the chemical will kill
the microbes; use it rarely or never.
-- Warning means that limited use should not
affect the system much.
-- Caution typically means that the product
will have little effect on the system.
▶▶ Excessive amounts of toilet paper cause sludge to
build up faster.
▶▶ Treated toilet paper, such as the type that contains lotion, does not settle well and forms a
thick layer of scum at the top of the tank.
▶▶ Other paper products, such as wet wipes, should
not enter the system.
▶▶ Flushable cleaning products, many wipes and
toilet cleaning materials are labeled as “septic safe.” This statement typically refers to
their ability to flow through the piping. These
items will collect in the treatment system and
increase the need for maintenance.
▶▶ Trash and nondigestible material increase the
amount of maintenance required and may even
shorten the life of the components. Examples
are rags, toys, diapers, condoms, cat litter,
plastic bags, coffee grounds, cigarette filters,
and feminine hygiene products. Many of these
items have neutral buoyancy and will pass
through the treatment components. Cat litter
and coffee grounds add to the sludge that must
be pumped out during maintenance. Diapers
must be removed individually.
Make a list of the cleaning and antibacterial products used in your home. When using these products,
keep in mind that they can have a cumulative effect
on the treatment system. If something will harm the
microbes in the system, do not send it down the drain.
Preventing rainwater from overloading the system
An onsite wastewater treatment system is
designed to handle a specific volume of wastewater.
If rainwater
enters the system, the proper operation can be disrupted.
Water collecting over the components can leak
into them. Also, the tanks are installed in an excavation that is backfilled with material that can collect
water. If the system is not watertight, the collected
water can enter the system and flush sewage through
the treatment system and into the yard.
Evaluate these conditions to determine whether
rainfall may be affecting the system:
▶▶ Look at the ground over the tanks to see if
a depression has developed where rainwater
could accumulate. Rainwater infiltrating the
system can overload the treatment components.
▶▶ Evaluate the color and growth of grass around
the tank. Excessive growth and darker green
color than the other grass in the yard indicates
that the tank or piping is broken.
▶▶ If the tank has a riser, verify that it is in good
condition and properly sealed to prevent
infiltration.
▶▶ Check the inside of the riser/tank seams for
stains that would indicate that groundwater or
surface water is entering the tank.
▶▶ Evaluate the system performance during rainy
periods: Rainwater may be infiltrating the
system if there is an unexplained number of
dosing cycles or water flow and/or if the spray
distribution system is spraying during a rain
shower.
Protecting your family and pets
Returning after vacation
An onsite wastewater treatment system is treating sewage using containers to hold the wastewater,
microbes to remove contaminants, electrical components to move air and water and sense water levels,
electricity to power the electrical components, and
chlorine/UV radiation to disinfect the wastewater.
By their nature, these parts and components pose a
risk to public health, environmental health, public
A vacation or extended absence develops a condition of limited food supply in the wastewater treatment system. The microbial population is reduced,
which also reduces treatment once the vacationer
returns and wastewater addition resumes. Therefore,
the wastewater loading should be increased gradually
for the first couple of days, which allows the microbial
population to grow. Avoid greater than average water
7
safety, and pet safety. If the system components
are in areas often visited by your pets and family,
greater attention is needed when selecting treatment
system components, implementing component safeguards, keeping chlorine disinfectant in the unit,
and keeping the components functioning properly,
which may include upgrading existing systems.
Reduce these risks by limiting access to these
components. Safety practices include installing fencing for components, risers with heavy concrete lids,
lighter lids with safety screws, lighter lids with locking mechanisms, lighter lids with internal restrictions to access, and control panels with screws and/
or locks.
Use products only in accordance with the
instructions on their labels. As the system owner,
you are responsible for following these safety practices.
Troubleshooting
Troubleshooting involves identifying and correcting sources of system breakdown. If a component is found to be inoperable during an inspection,
troubleshooting is often required to bring it back to
into operation. Contact a trained professional maintenance provider to identify and fix the problem.
For more information
A comprehensive guide for homeowners, Checking My Aerobic System: General Guidance for Monitoring Aerobic Treatment Units, Disinfection Units,
and Spray Fields in Texas, is available at the Texas
AgriLife Extension Service Bookstore at https://
agrilifebookstore.org. Also available at that site is
Onsite Wastewater Treatment Systems: Responding
to Power Outages and Floods.
This publication was funded, in part, by the Rio Grande Basin Initiative administered by the Texas Water Resources
Institute of Texas AgriLife Extension Service, with funds provided through a grant from the National Institute
of Food and Agriculture, U.S. Department of Agriculture, under Agreement No. 2009-45049-05492.
The information given herein is for educational purposes only. Reference to commercial products or trade names is made
with the understanding that no discrimination is intended and no endorsement by the Texas AgriLife Extension Service is implied.
Produced by AgriLife Communications, The Texas A&M System
Extension publications can be found on the Web at: http://AgriLifebookstore.org
Visit the Texas AgriLife Extension Service at http://AgriLifeextension.tamu.edu
Educational programs of the Texas AgriLife Extension Service are open to all people without regard to socioeconomic level, race, color, sex, disability, religion,
age, or national origin.
Issued in furtherance of Cooperative Extension Work in Agriculture and Home Economics, Acts of Congress of May 8, 1914, as amended, and June 30, 1914,
in cooperation with the United States Department of Agriculture. Edward G. Smith, Director, Texas AgriLife Extension Service, The Texas A&M System.
5M, New